to prevent UDF calculation Range is empty

i have UDF for sum (A2-A1)+(A3-A2)+(A4-A3) + ... So on
when i am select =adc(A1:A5) result is true
but while 1 am select adc(A1:A11) result not correct
A1:A11 is empty
i has to use if for prevent calculation but not sukses
help me every body

Function adc(r As Range)
Dim x, i&, s&: x = r.Value
On Error Resume Next
   For i = 1 To UBound(x, 1)
        If (x(i, 1)) > 0 Or x(i, 1) <> Empty Then
          If s = 0 Then
               s = Val(x(i + 1, 1)) - Val(x(i, 1))
          Else
               s = s + Val(x(i + 1, 1)) - Val(x(i, 1))
          End If
        End If
   Next i
adc = s
End Function

res.png
IN this picture result 40 is true but result -10 not true

Is this the actual calculation, or is this an attempt at something that you feel is representative? Some simple algebra on that expression should show you that sum(for i= 1 to n-1)(a(i+1)-a(i)) simplifies to a(n)-a(1) [50-10 in the example]. Assuming your example is representative, I would be tempted to do away with the UDF and do something like =INDEX($A$1:$A$11,COUNT($A$1:$A$11)-$A$1

I don't understand your response.

If this is not the actual calculation you are using, I suggest that you provide a sample of the actual calculation.

If this is the actual calculation, but you are working with varying numbers of entries, I don't understand why the simpler, non-VBA formula I provided wouldn't work, as it is designed to handle varying numbers of entries in A1:A11.

I can't see the point either, but perhaps

Function adc(r As Range)
Dim x, i&, s&: x = r.Value
On Error Resume Next
   For i = 2 To UBound(x, 1)
        If (x(i, 1)) > 0 Then
            s = s + Val(x(i, 1)) - Val(x(i - 1, 1))
        End If
   Next i
adc = s
End Function